Compensation mechanism for component and assembly deviation in an component precision positioning stage

ABSTRACT

A compensation mechanism for correcting component fabrication and assembly deviations in component precision positioning stages utilizing a planar mounting table arranged to slide between two rails consisting of a pair of grooves disposed adjacent one edge of the table and a single groove adjacent an opposite edge of the table, a spring arrangement forming slot being provided in close proximity to opposite edge to provide spring bias of the grooves against the rails.

RELATED APPLICATION

[0001] This is a continuation-in-part application of U.S. patentapplication Ser. No. 09/667,035 filed Sep. 21, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention resides in the field of adjustable workpiecemounting stages and more particularly relates to a modification in themounting table to which the work pieces are attached to compensate forminor deviations in component fabrication and stage assembly.

[0004] 2. Description of the Prior Art

[0005] Precision positioning stages of the type relating to theinvention are disclosed in U.S. Pat. Nos. 4,652,095 and 5,077,620 issuedto the applicant. In the first of these, the device described employs anadhesive assembly concept for a stage utilizing two end plates havinggrooves for receiving a pair of parallel smooth cylindrical rails and amounting table slidably disposed between the plates.

[0006] In the second of these, which is an improvement of the first,there is disclosed an electrical motor, gear system, and encoder mountedon an additional plate also disposed between the rails, the motor beingoperationally connected to the mounting table by a threaded rod suchthat the table is moved by actuation of the motor.

[0007] In the manufacture and construction of these precision devices,great care must be taken in fabricating the component parts andassembling them into a finished unit. Some tolerances must be within oneor two ten-thousandths of an inch for both fabrication and assembly inorder to achieve a unit which will function properly over a period oftime. It has been found that even the most rigorous shop standards willnot prevent the limited performance and possible failure of a percentageof units which is greater than desirable. Further, additional unitswhich function well upon delivery will, over a period of time, wear tothe point of unacceptable performance. The present invention is intendedto alleviate the above mentioned problems in the interaction of the twomain components of these stages, i.e. the rails and the mounting tablewhich moves between them. This is accomplished by a modification to themounting table providing a take-up mechanism to compensate for minordeviations in component fabrication and assembly.

SUMMARY OF THE INVENTION

[0008] The invention may be summarized as a compensation or take-upmechanism to reduce the requirement for extreme accuracy in the subjectstages, to prevent excessive looseness or tightness in the back andforth motion of the mounting table on the rails, to prevent jogging,i.e. abrupt or non-linear motion of the table and generally to provide acushioned fit between the table and the rails. The above objectives areachieved by disposing a pair of spaced projections, each having a grooveat one edge of the table to engage one of the rails and a singleprojection, having a groove, intermediate the pair of spaced projectionsat the opposite edge of the table to engage the other of the rails. Thegrooves are arranged to be substantially parallel to the upper and lowerplanar surfaces of the table. An elongate slit parallel to the rails anddisposed adjacent to the single projection forms a leaf springarrangement urging the grooves into engagement with the rails, the tablebeing constructed of metal or plastic chosen to provide the desiredspring action.

[0009] According to the invention there is provided an componentprecision positioning stage, comprising a pair of straight smoothunthreaded rails secured in spaced apart parallel relationship, acomponent mounting table slidably mounted to and disposed over saidrails, said mounting table being a planar rectangular member havingthree inwardly facing rail engaging grooved projections disposedadjacent opposing edges of the table, two said grooved projections beingspaced apart on one of said opposing edges and engaging one of the railsand the other of the grooved projections being centrally positionedadjacent the other of the opposing edges and engaging the other of therails, and a slot in said table, closed at its ends, parallel to and inclose proximity to the opposing edge of the other of the groovedprojections, to define a leaf spring arrangement biasing the groovedprojections together whereby grooves of the grooved projectionsresiliently engage the rails.

[0010] Preferably the table has a central threaded bore positioned toengage a threaded rod adapted to be driven by a stage drive means, thethree grooved projections form a triangle of rail engaging locations onthe table with said two grooved projections disposed at one opposingedge of the table and the slot extends to closely adjacent the opposedends of the table.

[0011] Also according the invention there is provided a precisioncomponent positioning stage comprising:

[0012] a) first and second smooth straight unthreaded cylindrical railssupported in spaced apart parallel relationship;

[0013] b) a component mounting table defining first and second groovesspaced along and engaging said first rail and defining a third grooveintermediate of the first and second grooves and engaging said secondrail; and

[0014] c) a pair of cantilever springs defined by the table to bias saidgrooves inwardly into engagement with said rails whereby deviations froma true linear path are prevented by said bias.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention will now be described, by way of example, withreference to the accompanying drawings, in which:

[0016]FIG. 1 is a plan view of a positioning stage incorporating thefirst embodiment of the invention;

[0017]FIG. 2 is a cross-section of one of the rail engaging grooves ofthe table 22 of FIG. 1 taken on section line 2-2 of FIG. 1;

[0018]FIG. 3 is a perspective view of a second embodiment of a table ofa positioning stage shown in FIG. 1; and

[0019]FIG. 4 is a plan view of a portion of the positioning stage of thepresent invention with the table shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020]FIG. 1 illustrates the preferred embodiment of the invention asutilized in a precision positioning stage employing an electric motorfor moving the mounting table. Smooth cylindrical parallel rails 10, 12are spaced apart by and adhesively attached to end plates 14, 16 ingrooves 18, 20, respectively. Component mounting table 22 having threeprojections 23, each defining a rail receiving groove, is slidablydisposed between rails 10, 12. The projections 23 consist of twoprojections spaced apart on one longitudinal edge 24 of the table toengage rail 10 adjacent opposite ends 25 of the table, and a singleprojection located centrally on the opposite longitudinal edge 26 of thetable to engage rail 12 centrally intermediate the ends 25. A fixedmotor assembly mounting plate 27 is attached to rails 10, 12. Partiallythreaded rod 28 extends through end plate 16, is threadably engaged withmounting table 22 and is rotationally connected to end plate 14 by clamp28.

[0021] Motor assembly 30, consisting of electric motor 32, motorrevolution sensing encoder 34, and speed reduction gear train 36, ismounted on plate 27. Rotation of the motor, electrically energizedthrough cable 38, rotates rod 28 and moves table 22 back and forthbetween end plates 14, 16 along the rails 10, 12.

[0022] As the scale of the above described device is extremely small,the table being approximately one-half inch square and 0.2 inches thickwith the extent of mounting table travel being in the vicinity of one totwo inches, it will be seen that the tolerance of component fabricationand assembly is quite critical for smooth and accurate operation.Disposition of slit 40, approximately 0.008 inch wide, extending throughthe table 22 in close proximity to longitudinal edge 26 provides ameasure of compensation for manufacturing inaccuracies which has beenfound to greatly increase the acceptability of finished units ascompared to stages without the present invention. This slit 40 extendsparallel to rail 12 for a substantial portion of the length of the table22 between ends 25 thereby to form a leaf spring 44 parallel to rail 12and edge 26, arranged to urge the grooves into engagement with therespective rails 10, 12 with a force of about one pound. The slit may bemachined by EDM and EDM wire threading openings may be provided at theends of the slit, as illustrated.

[0023]FIG. 2 provides an enlarged view of the groove of one of theprojections 23, all three of which are identical in cross-section. Inparticular FIG. 2 illustrates the positioning of the grooves betweenupper and lower surfaces 46, 48 of table 22.

[0024] Each groove comprises two rail engaging faces 50, 52 disposed at45° to the surfaces 46, 48 and spaced by a vertical surface 54 spacedfrom the rail engaging surfaces 50, 52.

[0025] Surfaces 56, 58, parallel with surfaces 46, 48, extend over theassociated rail in spaced relationship thereto to ensure retention ofthe table 22 on the rails 10, 12.

[0026] It has been found that this invention's use of three groovedprojections in the arrangement described provides compensation of thetable on the rails equal to that of prior art designs while the springbias action is greatly facilitated by the slit design also described.

[0027]FIGS. 3 and 4 illustrate a second embodiment in which the table 22fits over the rails 10, 12 instead of between them. Except as nowdescribed, the features of the second embodiment are similar to thefirst embodiment and will not again be described here.

[0028] The component mounting table 22, has three inwardly facingprojections 23, formed on downwardly extending side parts of the table,each defining a rail receiving groove, is slidably mounted on the rails10, 12. The projections 23 consist of two projections spaced apartadjacent one longitudinal edge 24 of the table to engage rail 10adjacent opposite ends 25 of the table, and a single split projectionlocated centrally on the opposite longitudinal edge 26 of the table toengage rail 12 centrally intermediate the ends 25. A partially threadedrod 28 (not shown in FIGS. 3 and 4) is threadably engaged with mountingtable 22 and is rotationally connected to plate 14 by a clamp 29 (seeFIG. 1).

[0029] A slot 40, closed at both ends and approximately 0.008 inch wide,extends through the table 22, is disposed in close proximity to thelongitudinal edge 26 to provide a measure of compensation formanufacturing inaccuracies and has been found to greatly increase theacceptability of finished units as compared to stages without thepresent invention. This slot 40 is centered on the single projection andextends parallel to rail 12 for a substantial portion of the length ofthe table 22 between ends 25 thereby to form a pair of cantileversprings 60 parallel to rail 12 and edge 26 and separated by a verticalslot 62 centrally disposed in the adjacent projection 23. The leafsprings are arranged to urge the grooves into engagement with therespective rails 10, 12 with a force of about one pound.

[0030] The second embodiment allows a wider disposition of the tablesupport points on the rails and an increase in the table length (up totwice that length of the table of the first embodiment). Assembly of thestage is also simplified.

1. An component precision positioning stage, comprising a pair ofstraight smooth unthreaded rails secured in spaced apart parallelrelationship, a component mounting table slidably mounted to anddisposed over said rails, said mounting table being a planar rectangularmember having three inwardly facing rail engaging grooved projectionsdisposed adjacent opposing edges of the table, two said groovedprojections being spaced apart on one of said opposing edges andengaging one of the rails and the other of the grooved projections beingcentrally positioned adjacent the other of the opposing edges andengaging the other of the rails, and a slot in said table, closed at itsends, parallel to and in close proximity to the opposing edge of theother of the grooved projections, to define a leaf spring arrangementbiasing the grooved projections together whereby grooves of the groovedprojections resiliently engage the rails.
 2. The stage of claim 1wherein said table has a central threaded bore positioned to engage athreaded rod adapted to be driven by a stage drive means.
 3. The stageof claim 1 wherein the three grooved projections form a triangle of railengaging locations on the table with said two grooved projectionsdisposed adjacent one opposing edge of the table.
 4. The stage of claim3 wherein the slot extends to closely adjacent the opposed ends of thetable.
 5. The stage of claim 4, wherein the slot defines two cantileversprings forming the spring arrangement and being formed by a slitlocated centrally of the other of the grooved projections.
 6. Aprecision component positioning stage comprising: a) first and secondsmooth straight unthreaded cylindrical rails supported in spaced apartparallel relationship; b) a component mounting table defining first andsecond grooves spaced along and engaging said first rail and defining athird groove intermediate of the first and second grooves and engagingsaid second rail; and c) a pair of cantilever springs defined by thetable to bias said grooves inwardly into engagement with said railswhereby deviations from a true linear path are prevented by said bias.7. The stage of claim 6 comprising means for moving the table along therails.
 8. The stage of claim 6 wherein the cantilever springs are formedby a slot in the table closed at both ends and separated by an openingcentered on the third groove, the slot being disposed parallel to,closely adjacent the third groove and centered on the third groove.